Delta printer without endstop switches
Posted by dc42
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Delta printer without endstop switches July 24, 2015 12:24PM |
Registered: 10 years ago Posts: 14,684 |
It occurred to me that a delta printer using Duet electronics and a Z probe could be made to work without endstop switches. The principle would be:
* Use rubber pads at the top of the carriages, so that they bump into the top corner pieces softly.
* Change the homedelta.g file to reduce motor current at the start (M906 command) so that the carriages don't slam hard into the corners, then move all 3 towers up far enough to guarantee that they reach the endstops (G1 S2 command). Then move the carriages down a few mm, then restore the motor current to normal.
This will give rise to a homing position uncertainty of +/- 2 full steps, which is typically +/-0.4mm using 1.8 deg/step motors. This is close enough to do Z probing. So:
* Probe one point in front of each tower and do 3 point auto calibration, to set the endstop corrections, thereby eliminating the homing uncertainty. This takes less than 10 seconds.
* If desired, do 4- or 6-point auto calibration to fine-tune the endstop corrections and set the delta radius and optionally the tower offset corrections.
The important thing is not to home again before printing, because that would re-introduce the homing position uncertainty.
There are some disadvantages to this approach, for example homing will take just as long no matter how high or low the effector is. But it might be useful for low-cost delta printer kits like RepRapPro's Fisher, as it would simplify assembly and reduce the amount of wiring.
Edited 1 time(s). Last edit at 07/24/2015 12:25PM by dc42.
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
* Use rubber pads at the top of the carriages, so that they bump into the top corner pieces softly.
* Change the homedelta.g file to reduce motor current at the start (M906 command) so that the carriages don't slam hard into the corners, then move all 3 towers up far enough to guarantee that they reach the endstops (G1 S2 command). Then move the carriages down a few mm, then restore the motor current to normal.
This will give rise to a homing position uncertainty of +/- 2 full steps, which is typically +/-0.4mm using 1.8 deg/step motors. This is close enough to do Z probing. So:
* Probe one point in front of each tower and do 3 point auto calibration, to set the endstop corrections, thereby eliminating the homing uncertainty. This takes less than 10 seconds.
* If desired, do 4- or 6-point auto calibration to fine-tune the endstop corrections and set the delta radius and optionally the tower offset corrections.
The important thing is not to home again before printing, because that would re-introduce the homing position uncertainty.
There are some disadvantages to this approach, for example homing will take just as long no matter how high or low the effector is. But it might be useful for low-cost delta printer kits like RepRapPro's Fisher, as it would simplify assembly and reduce the amount of wiring.
Edited 1 time(s). Last edit at 07/24/2015 12:25PM by dc42.
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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Re: Delta printer without endstop switches July 24, 2015 02:37PM |
Registered: 9 years ago Posts: 475 |
That is a good idea, I think It will be a great simplification and will make a lot less trouble both in the build, in commissioning and in operation. And that saves some cost, also.
The extra time to go up is really minor, this is a small printer.
For a light printer as the Fisher, the inertia of the moving parts is extremely low, so the impact on top with reduced current motors may not be that high.
Edited 2 time(s). Last edit at 07/24/2015 02:44PM by PRZ.
The extra time to go up is really minor, this is a small printer.
For a light printer as the Fisher, the inertia of the moving parts is extremely low, so the impact on top with reduced current motors may not be that high.
Edited 2 time(s). Last edit at 07/24/2015 02:44PM by PRZ.
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Re: Delta printer without endstop switches July 26, 2015 04:16PM |
Registered: 13 years ago Posts: 1,611 |
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Re: Delta printer without endstop switches July 31, 2015 09:04AM |
Registered: 10 years ago Posts: 14,684 |
Quote
droftarts
I'm pretty sure this has been used before; I've been told that this is the way some 3D Systems' printers home their axes! Though it sounds a bit 'agricultural' to me...
Ian
RepRapPro tech support
Maybe it is a bit 'agricultural'; but it avoids the possibility of endstop switches failing to trigger, which can be a problem in some designs, or wires falling off the switches. Also, I've seen a few posts on this forum about problems homing, which turned out to be caused by two of the endstop connectors being swapped where they plug in to the controller electronics. So using this approach could make thing easier for support engineers like you!
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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